A hydrogel is basically a polymer, with high affinity for water, that has swelled in an aqueous solvent. Hydrogels have various useful properties including sufficient water absorbance, swellability, adhesiveness, and electrical conductivity. The hydrogel relies on these properties for its wide-ranging applications in civil engineering and construction, agriculture and horticulture, food industry, medical and pharmaceutical industry, cosmetics, electricity, and other fields.
For example, in medical practice, adhesive hydrogel is used as electrode pads for electrocardiogram instrumentation. Recently, it is also used as electrode pads for EMS (electrical muscle stimulation) devices in weight reduction and muscle training. An EMS device is an exercise machine that applies electrical stimulation to the skin through adhesive hydrogel electrode pads adhering to the skin, causing muscle to contract. The EMS device has seen increasing opportunities to be used in general households.
The adhesive hydrogel used for these electrode pads need to be capable of exerting a high adhesive strength onto the skin.
Patent Document 1, as an example, discloses technology to improve the adhesive strength of an adhesive hydrogel by using a water-soluble polymer in a predetermined quantity and also discloses medical electrodes fabricated from the adhesive hydrogel.
However, the hydrogel disclosed in Patent Document 1 quickly loses much of its adhesive strength over mere several times of attaching and peeling-off. The hydrogel disclosed in Patent Document 1 fails to deliver sufficient adhesive strength after being used repeatedly. The primary reason for the hydrogel reducing its adhesive strength after being used repeatedly would be the horn coming off the skin surface and sticking to the surface of the electrode pad when the electrode pad is peeled from the skin, which practically reduces the effective adhesive area of the electrode pad.
The hydrogel disclosed in Patent Document 1 has a major problem that even if it can have its initial adhesive strength improved, it still loses an appreciable proportion of its adhesive strength after being used repeatedly.
To maintain the adhesive strength of the hydrogel over repeated use, Patent Document 2, as an example, discloses technology to restore the adhesive strength of the hydrogel by washing, in water, the adhesive surface of the hydrogel which has reduced its adhesive strength over several times of attaching to, and peeling from, the skin.
The hydrogel described in Patent Document 2 requires washing in water and other manual processes. To ensure restoration of the adhesive strength of the hydrogel, the user needs to follow various instructions given in the product manual as to, for example, how the hydrogel should be washed and dried, which the user would find too complicated and laborious.
The hydrogel disclosed in Patent Document 2 also has a problem that even if it can have its initial adhesive strength improved, it still loses an appreciable proportion of its adhesive strength after being used repeatedly.